The present invention relates generally to intramedullary nails used for treatment of a fracture of a bone having a medullary canal extending longitudinally within the bone and, more particularly, to the structure of the intramedullary nail and/or spacer and methods for anchoring the intramedullary nail and spacers with respect to one or more fragments of the fractured bone.
Intramedullary nails are used by orthopaedic surgeons to treat fractures involving long bones such as the femur, humerus, tibia, fibula, and others. In such treatment, the medullary canal of the various fragments or pieces of the fractured bone is drilled out, reamed, or otherwise opened from one end. The intramedullary nail is then longitudinally placed in the medullary canal to contact at least two of the fragments, i.e. such that the nail extends on both sides of the fracture. As used herein, the term xe2x80x9cfragmentxe2x80x9d refers to a portion of a fractured bone regardless of whether the fracture is complete. When implanted, the intramedullary nail supports and strengthens fragments of the fractured bone during healing of the fracture.
Various types of intramedullary nails are well known within the medical device arts, and several different methods have been used to attach the intramedullary nail to and within the bone. As an example, in U.S. Pat. No. 4,338,926 to Kummer et al., an intramedullary nail is shown that provides a compressive force radially outward on an interior wall of the cortex structure surrounding the intramedullary nail. The compressive force secures the Kummer intramedullary nail within the medullary canal of the fragments. Similarly, in U.S. Pat. No. 5,514,137 to Coutts, cement is injected through a cannula in an intramedullary nail to the bone. Other intramedullary nails employ a more secure and mechanically positive attachment to the bone, such as through the use of one or more bone fasteners that extend generally transversely to the longitudinal axis of the intramedullary nail and through the cortex of the bone. The bone fasteners is received within a receiving recess or through-hole within the intramedullary nail to secure the intramedullary nail relative to the bone fastener. In a transverse attachment, the receiving opening of the intramedullary nail defines an axis that is at an angle to the longitudinal axis of the nail (commonly at 45xc2x0 and 90xc2x0 angles), and the bone fastener is advance on this receiving opening axis. U.S. Pat. No. 4,733,654 to Marino, U.S. Pat. No. 5,057,110 to Kranz et al., U.S. Pat. No. 5,127,913 to Thomas, Jr., U.S. Pat. No. 5,514,137 to Coutts (proximal end) and others disclose such a transverse bone fastener attachment in a bicortical attachment. U.S. Pat. No. 5,484,438 to Pennig shows a nail design with a recess that permits only unicortical attachment. The subject invention particularly pertains to intramedullary nails that utilize bone fasteners transversely through the cortex for attachment.
Problems may arise when attaching an intramedullary nail to a fragment with a bone fastener. It is occasionally difficult for the surgeon to properly align the bone fastener and/or a hole for the bone fastener with the receiving opening in the intramedullary nail. Part of the alignment problems is simply due to difficulty in aligning the bone fastener with the receiving opening when the receiving opening is within the bone. Additionally, the intramedullary nail may be slightly bent or distorted during insertion thereof into the medullary canal. Such bending and/or distortion may be desired in some instances so that the shape of the inserted intramedullary nail better matches the particular shape of the medullary canal for a particular patient.
Regardless of whether intended or unintended, such bending or distortion of the intramedullary nail creates further alignment errors between the bone fastener and/or a hole for the bone fastener and the receiving opening on the nail. Four types of alignment errors can be identified: (a) in transverse displacement (e.g., when the axis of the bone fastener is in the same transverse plane as the receiving opening in the intramedullary nail but does not intersect the axis of the intramedullary nail); (b) in longitudinal displacement (i.e., when the bone fastener is at a different longitudinal location than the receiving opening in the intramedullary nail); (c) in longitudinal angular misalignment (i.e., when the axis of the receiving opening and the axis of the bone fastener are at different angles relative to the longitudinal axis of the intramedullary nail); and (d) in transverse angular misalignment (i.e., when the axis of the receiving opening and the axis of the bone fastener are in the same transverse plane but at different radial positions relative to the intramedullary nail.
In view of the above, various types of jigs have been proposed to reduce alignment errors, such as shown in U.S. Pat. No. 4,733,654 to Marino and U.S. Pat. No. 5,776,194 to Mikol et al. Such jigs may be temporarily attached to the proximal end of the intramedullary nail to help align the bone fastener and/or the drill to the receiving opening in the intramedullary nail. While such jigs are helpful, the jigs become less reliable as distance from the proximal end of the intramedullary nail increases, particularly if any bending of the intramedullary nail has occurred. Additional solutions are needed, especially for attaching the distal end of the intramedullary nail to a distal fragment.
Another method to reduce such alignment problems is to locate the receiving opening(s) in-situ, such as through an x-ray or the use of magnets as taught in U.S. Pat. No. 5,127,913 to Thomas, Jr. Such methods are not typically preferred by surgeons in as much as the methods require significant additional time and effort during the orthopaedic surgery, to the detriment of the patient.
A third method to reduce such alignment problems is to drill the receiving opening into the intramedullary nail only after the intramedullary nail is placed into the bone, allowing the receiving opening to be formed at a range of locations. Such in-situ drilling is disclosed in U.S. Pat. No. 5,057,110 to Krans et al., wherein a tip section of the intramedullary nail is formed of a bioresorbable material. Bioresorbable materials, however, are not as strong as metals, leading to an intramedullary nail that is weaker than desired and has a weaker attachment than desired.
Further problems with intramedullary nails occur during placement of the intramedullary nail. For minimal damage to cortical tissue of the bone and most beneficial to healing, both the hole that is drilled in the medullary canal for the intramedullary nail and then the intramedullary nail itself, need to be precisely located and secured with respect to the medullary canal.
Additional problems with intramedullary nails occur due to the healing requirements of a bone with respect to the strength and rigidity of the intramedullary nail. U.S. Pat. No. 4,756,307 to Crowninshield and U.S. Pat. No. 4,338,926 to Kummer et al. disclose intramedullary nails with bioresorbable portions to weaken the mail relative to the bone over time. These intramedullary nails, however, forsake the use of a transverse bone fastener to achieve the benefit of the bioresorbable portions.
It would thus be advantageous to provide an intramedullary nail that overcomes the above-noted shortcomings. It would be further advantageous to provide an intramedullary nail and related portions and/or components that overcome the above-noted and other shortcomings.
The subject invention is an intramedullary nail for treatment of a fracture of a bone by placement of the intramedullary nail within the medullary canal of the fractured bone. The intramedullary nail is formed with at least one opening in an exterior side that is adapted to receive a spacer or window insert of a non-metal material. The opening and window insert have cooperating structures that provide a spring type elastic fit, snap-fit, and/or interference fit of the window insert within the opening. The nail is used with a bone fastener such as a bone screw that is advanced transversely through the bone and into the spacer, preferably in a bicortical attachment with the bone.
The bone fastener is smaller across than the window insert so that the window insert spaces the bone fastener relative to the metal structure of the intramedullary nail. The opening may have a longitudinal length that is different from its width, while the bone fastener has a circular length. Because the bone fastener is smaller across than the opening and the window insert, a larger error in placement of the bone fastener is permissible.
In one form, there is provided an intramedullary nail for treatment of a fracture of a bone having a medullary canal extending longitudinally. The intramedullary nail includes a nail structure and a window insert. The nail structure has a longitudinal nail body defining a distal end and a proximate end. The nail body has a dynamization opening in one of the distal end and the proximate end. The dynamization opening has a first interference receptor disposed in a wall of the dynamization opening and a second interference receptor disposed in the wall. The window insert is formed of a non-metal material and is adapted to be inserted into the dynamization opening. The window insert has a window insert body having a first interference extending from a first surface of the window insert body and a second interference extending from a second surface of the window insert body. The first and second interferences are adapted to be received in the first and second interference receptors of the dynamization opening respectively upon insertion of the window insert into the dynamization opening.
In another form, there is provided an intramedullary nail for treatment of a fracture of a bone having a medullary canal extending longitudinally. The intramedullary nail is defined by a longitudinal nail body. The longitudinal nail body defines a distal end and a proximate end, with the nail body having a dynamization opening extending through the nail body at one of the distal end and the proximate end essentially transverse to a longitudinal axis of the nail body. The dynamization opening is defined by an oval wall with the oval wall having a first groove positioned essentially parallel to the longitudinal axis and a second groove disposed diametrically opposite the first groove and essentially parallel to the longitudinal axis. The dynamization window insert is formed of a non-metal material and is adapted to be inserted into the dynamization opening. The window insert has an oval window insert body having a first rail extending a first distance from a first surface of the window insert body and a second rail extending a second distance from a second surface of the window insert body. The first and second rails are adapted to be received in the first and second grooves of the dynamization opening respectively upon insertion of the dynamization window insert into the dynamization opening.
In yet another form, there is provided a window insert for a dynamization opening of an intramedullary nail. The window insert has an oval body defining a top and bottom surface, a first and second side surface, and a first and second curved side. A first rail is disposed on the first side and extends a first distance therefrom. A second rail is disposed on the second side and extends a second distance therefrom.
In still another form, there is provided a method of retaining bone fragments. The method includes the steps of: (a) placing a dynamization window insert in a dynamization opening of an intramedullary nail, the intramedullary nail having a longitudinal nail body defining a distal end and a proximate end, the dynamization opening extending through the nail body at one of the distal end and the proximate end essentially transverse to a longitudinal axis of the nail body, the dynamization opening defined by an oval wall, the oval wall having a first groove positioned essentially parallel to the longitudinal axis and a second groove disposed diametrically opposite the first groove and essentially parallel to the longitudinal axis, the dynamization window insert formed of a non-metal material and adapted to be inserted into the dynamization opening, the window insert having an oval window insert body having a first rail extending a first distance from a first surface of the window insert body and a second rail extending a second distance from a second surface of the window insert body, said first and second rails adapted to be received in the first and second grooves of the dynamization opening respectively upon insertion of the dynamization window insert into the dynamization opening; (b) placing the intramedullary nail through the bone fragments, and (c) inserting a bone fastener through the dynamization window insert.
In a yet further form, there is provided a bone support assembly for treatment of a bone. The bone support assembly includes a bone support implant formed of a non-resorbable material, and a first window insert formed of a non-metal material. The bone support implant has a first opening defined therein. The first opening has a first opening shape including a narrow portion adjacent an outer surface of the bone support implant and a wider portion more interior the bone support implant. The first window insert has outer dimensions that correspond to the first opening. The first window insert has a first section that mates with the narrow portion of the first opening. The first window insert has a second section wider than the first section that mates with the wider portion of the first opening more interior of the bone support implant. In this manner, the second section of the first window insert is wider than the narrow portion of the first opening and serves to positively secure the first window insert in the first opening with an interference fit.